This invention relates to an improved synthetic turf surface for grass-type game playing fields.
Synthetic turf game playing surfaces typically are formed of carpets having upright piles or strands that are fastened to a base or backing sheet. The strands may be formed of thin, flat, narrow strips of suitable plastic material which may be gathered into tufts that are fastened to the base sheet. Commonly, the base sheet is formed of a woven cloth, made of a suitable plastic fabric, with a resilient coating or binder applied to the base sheet for anchoring the strands thereto. The detailed construction of such pile carpets varied considerably. However, in general, they are made of a weather resistant or outdoor type of construction.
Such carpets are usually laid upon a prepared, flat ground surface to form a game playing field which is intended to simulate a natural grass playing field surface. For some types of games, a resilient underpad is placed beneath the carpet and upon the firm ground support surface to provide a shock absorbing effect. Also, in some instances, a layer of sand or other particulate material is placed upon the upper surface of the carpet base sheet and around the strands. An example of this type of construction is shown in U.S. Pat. No. 4,389,435 issued Jun. 21, 1983 to Frederick T. Haas, Jr. Another example is shown in U.S. Pat. No. 4,637,942 issued Jan. 20, 1987 to Seymour A. Tomarin.
Further, examples of artificial turfs which are formed with the grass-like carpet placed upon a resilient underpad are disclosed in U.S. Pat. No. 3,551,263 issued Dec. 29, 1970 to Carter et al., which discloses a polyurethane foam underpad; U.S. Pat. No. 3,332,828 issued Jul. 25, 1967 to Faria et al., which discloses a PVC foam plastic or polyurethane foam plastic underpad; U.S. Pat. No. 4,637,942 issued Jan. 20, 1987 to Seymour A. Tomarin which discloses a rubber-like underpad; U.S. Pat. No. 4,882,208 issued Nov. 21, 1989 to Hans-Urich Brietschidel, which illustrates a closed cell polyethylene foam underpad; U.S. Pat. No. 3,597,297 issued Aug. 3, 1971 to Theodore Buchholz et al., which discloses a polyurethane underpad having voids; and U.S. Pat. No. 4,505,960 issued Mar. 19, 1985 to James W. Leffingwell, which discloses shock absorbing pads made of foamed polyvinyl chloride, polyethylene, polyurethane, polypropylene, etc.
As these various prior patents demonstrate, there has been a search in the past for an underpad material and construction which, when combined with a suitable synthetic blade forming carpet, provide a game playing surface which very closely simulates the feel and action and reaction effect of a natural grass playing field surface. The large variety of materials disclosed in the foregoing patents demonstrate that such a synthetic turf playing surface had not been found.
The present invention relates to a particular plastic underpad surface combined with an artificial grass forming carpet which very closely simulates a natural grass field which is particularly close in feel and performance to the natural grass portions of a typical golf course, as well as being very similar to other natural grass surface game playing fields.
This invention contemplates combining with a synthetic grass carpet a particular resilient polypropylene molded underpad which, together with the synthetic grass carpet, produces an effect which is strikingly similar to a natural grass playing surface formed particularly for golf courses. Thus, this invention contemplates utilizing expanded beads of polypropylene of a density of approximately between about 1.3 to 2.8 pounds per cubic foot molded into a thick sheet or pad of open cell structure with a density of between about 1.5 to 3 pounds per cubic foot. The combined turf carpet and supporting underpad effect may be enhanced by treating the free ends of the synthetic grass blades with a sandblast which splits or shreds the blade ends into fine slivers which intertwine and entangle with each other to form a dense mat upper surface upon the carpet.
An object of this invention is to provide an artificial turf with a particular resilient underpad formed of open cell, expanded beads polypropylene plastic which produces, as part of the turf surface, an effect which very closely simulates a natural grass playing field.